PALO ALTO, Calif. -- On Thursday night, from his position at outside linebacker, Stanford's Trent Murphy will angle himself opposite one of Oregon's offensive tackles and set his sights on Ducks signal-caller Marcus Mariota. Murphy's primary mission will be to sack the quarterback, something he has done 9 1/2 times this season and 26 times in his career.

"I put my hand [on] the ground, get my hips up in the air and it's like I'm going hunting," said the fifth-year senior. "I'm going after something. There's an end point I'm trying to get to, and there's someone trying to stop me. It's man versus man. It's my favorite thing to do."

Murphy is 6-foot-6 and 261 pounds, with long arms, nimble feet and a spin move he perfected as the 2009 Arizona state discus champion. He is the most fearsome member of the sixth-ranked Cardinal's veteran defense. A year ago, the unit led No. 14 Stanford to a 17-14 overtime upset of top-ranked Oregon, and it will look to produce a similar result against the second-ranked Ducks this Thursday. A consensus midseason All-America, Murphy -- who was recently named as one of 16 semifinalists for the Bednarik Award, given annually to the top defensive player in college football -- ranks third in the country in sacks and fifth in tackles for loss (13.5). He also has a pick-six and seven pass breakups or deflections, even though he plays primarily at the line of scrimmage.

Murphy plays with a deadly serious scowl wedged between his bald head and lightly grown beard. His expression doesn't change until after the final whistle -- and sometimes not even then. Fellow fifth-year Stanford linebacker and Butkus Award semifinalist Shayne Skov is a more recognizable player nationally, but head coach David Shaw didn't hesitate earlier this season when asked to name his team's "nastiest" defender.

"Trent's in his own category," said Shaw, "because there's really no off switch. It's just always on."

Added senior linebacker A.J. Tarpley this week: "[Murphy is] no different on the field than off the field. He's an aggressive guy. He's got that badass mentality. He's not mean in the sense that he's going to wrong you, but I wouldn't want to be on his bad side."

For those who think this is all hyperbole, a heavy dose of the kind of football cliché commonly used to describe a hard-nosed defensive player, consider Murphy's unique childhood, which involved steer wrestling, father-son self-defense lessons and a lot of really, really big people.

Murphy's father, Jerry, stands 6-7 and weighs 290 pounds. Now 52, he describes himself as the "runt" of his family. Jerry's two brothers are 6-9 and 6-10. His son Connor is only 16 but already stands 6-7. Jerry's daughter Kayli, a former basketball player at Arizona State, is 6-2.

"[Trent] comes from a bunch of big, mean suckers," said Jerry.

When Trent was young, Jerry, a plumbing contractor, moved his family to a large lot in the Lehi area of Mesa, Ariz. A recreational bodybuilder -- Jerry says he can still bench press 225 pounds 25 times -- he installed a 1,200-square foot weight room behind the house. His six children began working out when they were as young as four years old.

Jerry's lessons in toughness extended beyond weight training. He also emphasized self-defense. Trent recalls a day when he was outside in the yard after a workout and his father took off his shirt and tossed him a stick. "Pretend that stick's a knife," Jerry told him. "Try to stab me." When Trent did as he was told, Jerry immediately wrapped his shirt around the stick and snatched it out of Trent's hand.

"I teach my kids to take care of themselves," said Jerry. "[Trent is] not going to stand there and be your b----. Be a gentlemen, open doors for women, but when s--- hits the fan, he wants to whip you."

With more than an acre and a half of land, Jerry and his wife Laurie began buying horses. They eventually owned eight, in addition to their four dogs. The family also built a rodeo arena on their property, and Trent joined his father in team-roping competitions. When Trent wanted to impress visiting friends, he'd wrestle the steer calf that he and Jerry used for roping, which weighed more than 400 pounds.

"You're running full speed [on a horse] at the steer, and you drop onto the steer's head, place one hand under the jaw, one under the horn, twist his head to stop his momentum, and he falls onto his back," said Trent. "It's definitely a dangerous, dangerous sport."

Jerry describes his family as "hardworking, blue-collar Americans," and he lives by the motto, "No working, no eating." Trent was responsible for a long list of chores, including maintaining the family's expansive lawn. His father would inspect his work.

"One time I've got a couple big trash cans full of grass, dog poop, rotten oranges and everything you wouldn't want to see again," said Trent. "He walked out there, gave it a couple looks and said, 'No, not good enough,' and he went and dumped out both trash cans all over the yard and made me do it again. I've never been madder [in] my whole life, but it taught me a valuable lesson, to do it right the first time."

Murphy attended Brophy College Prep, a private Jesuit high school in Phoenix. During the football team's run to the 2005 state championship, coach Scooter Molander called up Murphy, then a lanky freshman, to play defensive end on the scout team. "Play after play after play, he would take on our offensive line, which averaged 265 pounds that year," said Molander. "He didn't have enough mass in his body to take that on and survive for five weeks, but he did, because he's tough."

Murphy made varsity the following season, and in 2007 he led the Broncos to another state title while playing defensive end and tight end. His weight training paid dividends. "He developed great speed over the years through hard work," said Molander, "but his core strength for a big guy was off the charts."

One of Murphy's most memorable moments at Brophy Prep did not come in a game. During his junior year, on the night before the Broncos' game at rival Mountain View High (the public school in Murphy's district), Montain View coaches noticed a person they believed to be Murphy doing up-downs on their field's 50-yard line. They told Molander, and he asked Murphy about it the next day, following the Broncos' 29-27 victory over the Toros.

"He said, 'I felt the need to work hard on the field we were going to win on,'" said Molander. "And he said, 'I wanted to leave a part of myself on this field.'" Murphy achieved that by doing up-downs until he vomited.

Coming out of high school, Murphy was 6-6 and 215 pounds. He was a three-star prospect, according to Rivals.com, who received scholarship offers from Arizona, Arizona State, Colorado and Utah. Stanford recruiter Lance Anderson, the Cardinal's outside linebackers coach, first noticed him during the spring of Murphy's sophomore year.

"We saw a guy that was so long, rangy and athletic, who was that long and that tall, and thought this guy is going to be able to do something," said Anderson.

Former Stanford coach Jim Harbaugh, who was then in the early stages of rebuilding the Cardinal program, placed an emphasis on recruiting tough guys. Murphy clearly fit the bill. "[Harbaugh] came and visited and saw the horses and stuff, that we kill our own cows around here," said Jerry. "He said, 'You guys are mean people. You're going to be just like your dad.'"

Shaw, who was Stanford's offensive coordinator at the time, said, "I don't know that we've seen a guy that played meaner in high school. He didn't just tackle guys, he tried to hurt them."

Five years and 45 pounds later, nothing has changed.

"[Trent is] going to legally punish the quarterback," said Tarpley. "When you see the quarterback, he's wincing as he gets up."

Murphy arrived at Stanford in 2009 along with Skov and defensive linemen Ben Gardner and Josh Mauro. All are now veterans on the Cardinal's defensive front. (Gardner is out for the rest of the season with a torn pectoral muscle.) Murphy redshirted as a freshman, and played just two games in 2010. As a sophomore, he had 6.5 sacks for Stanford's 2011 Fiesta Bowl team.

Shortly after that game -- a 41-38 overtime loss to Oklahoma State on Jan. 2 -- someone from the gang (believed to be the mullet-sporting Gardner) coined the phrase "Party in the Backfield." The expression quickly went viral on campus. (It's a commonly used Twitter hashtag on game days.) The Cardinal defense has embraced it. The unit led the nation in sacks last year (57) and is currently tied for the sixth most in the FBS this season (27). Murphy, in his first year as starter in 2012, had 10 sacks, the most of any Stanford player since linebacker Jon Alston had nine in '04. Through eight games this season, Murphy has already nearly matched his total from last fall.

"Knowing he's going to be the focal point of everybody's pass protection, he's still getting the job done," said Shaw. "It's a credit to him."

In the last two games, Murphy and the Cardinal defense have faced a pair of talented quarterbacks: UCLA's Brett Hundley, a projected first-round NFL draft pick, and Oregon State's Sean Mannion, the national leader in passing yards. Hundley entered the Bruins' Oct. 19 game against Stanford averaging 345.8 yards of total offense. He managed just 222 in a 24-10 Cardinal win. Mannion entered the Beavers' Oct. 26 clash with Stanford averaging 427.4 passing yards. He threw for only 271 in a 20-12 defeat.

Murphy, who lines up as both a hybrid linebacker and a defensive end in the Cardinal's 3-4 scheme (he moves to end in nickel situations), sacked Hundley twice and Mannion three times. But his impact on both games went beyond the box scores.

Against Oregon State, Murphy was constantly in the backfield. On one play late in the fourth quarter, he jumped the snap count so well that he actually got to Mannion too quickly. The quarterback was still dropping back, and he was able to spin away from Murphy and complete an 11-yard pass. Murphy also deflected two throws at the line of scrimmage and altered the path of several others, almost single-handedly taking away the Beavers' ability to throw short passes to his side of the field.

"For teams that want to throw those bubble screens and things on the perimeter, it's hard to throw those over him or around him," said Anderson. "He's so tall and he's so long and he has a great feel for when those things are coming."

Indeed, Murphy has returned two interceptions for touchdowns in his career, one last season against Washington and the other in September against Washington State. On both occasions, he was only a few feet from the quarterback. "I don't think quarterbacks are used to guys getting their hands up for those," Murphy said.

The game against Oregon on Thursday will be his biggest challenge of the season. Heisman hopeful Mariota has thrown for 2,281 yards and 20 touchdowns, with no interceptions, while also rushing for 511 yards (9.1 per carry) and nine scores. Murphy's job becomes particularly important against mobile quarterbacks, especially defending the shotgun zone-read. "For most of the night I'll have Mariota," Murphy said. "I'll be on the edge, trying to disrupt the backfield."

During last year's game in Eugene, Mariota burned the Cardinal for a 77-yard run in the first quarter. But he ran for just 12 yards the rest of the game, and he threw for only 207. Murphy had a sack, a pass breakup (nearly another interception at the line) and one critical play in overtime. On second-and-12 from Stanford's 27-yard line, Mariota faked a handoff and ran right. Murphy initially bit on the fake to the running back, but he quickly stepped back, changed direction and chased Mariota out of bounds after just a three-yard gain. Two plays later, Ducks kicker Alejandro Maldonado missed a 41-yard field goal, setting the stage for Cardinal kicker Jordan Williamson's 37-yard game-winner.

The teams that will meet on Thursday night are different, of course. Oregon has a new head coach (Mark Helfrich) and offensive coordinator (Scott Frost), and Mariota has become a far more dangerous passer. He has increased both his attempts-per-game (to 28.1 from 25.8) and yards-per-attempt (to 10.1 from 8.0) averages during the Ducks' 8-0 start. Stanford, meanwhile, will be playing its first game without Gardner (4.5 sacks, 7.5 tackles for loss). His absence will be somewhat offset by the return of veteran defensive end Henry Anderson, who will be playing for the first time since he suffered a leg injury during a win over Army in mid-September.

Murphy's mission will remain largely the same.

"My responsibility is to be a physical edge presence, to set the edge on the offense," he said. "I don't want to make a comparison between us and 300, but our outside 'backers will basically funnel them into the Hot Gates, which are the other nine defensive players."

It's a tall task, but one for which Murphy is seemingly well prepared. If anything, slowing Oregon's offense is child's play compared to some of the situations in which his father put him.

"If you dropped him off in the middle of nowhere with nothing but his underwear," said Jerry, "he'd find his way out."